In a clean room, it is essential keep some or all of the air in the room clean. Depending on the intended activity in the clean room, different levels of air cleanliness are required. In order to counteract contamination during activity in the room, such as surgery or production requiring a clean environment, it is of importance to reduce the number of airborne particles such as dust particles or bacteria-carrying particles, the latter also referred to as colony forming units (cfu).
The contamination level in a room may be defined in different ways. One example of a definition is the concentration of particles of a particular size. Some DIN (Deutsches Insitut für Normung) standards use this definition for defining a degree of protection for different clean rooms. For example, the maximum allowed degree of protection may be set to 3 500 particles/m3 for particles with a size up to 0.5 μm. Another example of a definition is the concentration of airborne bacteria carrying particles per volume. For example, the maximum allowed contamination level in a clean room may be defined as 100 cfu/m3.
Clean air may be provided using air supply systems providing turbulent air flows. One benefit of using a turbulent air flow is that the air present in the room comprising air borne particles is mixed with supplied clean air such that the present air is diluted. The contamination level of the room is thereby reduced.
For clean rooms requiring a higher level of cleanliness, such as high end production clean rooms or operating theatres for high infection sensitive surgery, the cleanliness requirements are much harder.
It should be noted that an air supply system arranged to provide a turbulent air flow in a room needs to achieve very high air flows, in the range of hundreds air exchange rates, to maintain such required low level of air borne particles. As a result, the provided clean room environment is not work friendly. To achieve a more work friendly environment and to reduce the amount of supplied clean air supply systems for providing laminar air flows are preferably used instead of air supply systems for providing on turbulent air flows. By using air supply systems based on laminar air flows, it is possible to keep the contamination level of the covered area low without the need for very high air flows.
U.S. Pat. No. 4,009,647 discloses an example of an apparatus for providing a clean air zone around a patient undergoing surgery. The apparatus comprises a plurality of air delivery means being adapted to supply air at different velocities.
WO 2008/136740 discloses a ventilating device for providing a zone of clean air between the ventilating device and a workplace region. The ventilating device comprises air supply units adapted to generate laminar air flows intended to constitute the clean air zone.
There is, however, a need to improve air supply systems for supplying clean air flows in a room.